Solid-state lighting devices employing light emitting diodes (LEDs) are increasingly useful for applications requiring robustness and long-life. For example, solid-state LEDs are found today in automotive applications. These devices are typically formed by combining multiple, small point-source LEDs into a single module together with glass lenses suitably designed to control the light as is desired for a particular application; see for example, WO99/57945, published Nov. 11, 1999. These multiple devices are expensive and complex to manufacture and integrate into single area illumination devices. Moreover, conventional LEDs provide point sources of light, a plurality of which are employed for area illumination.
Organic light emitting diodes (OLEDs) are manufactured by depositing organic semiconductor materials between electrodes on a substrate. This process enables the creation of light sources having extended surface area on a single substrate. The prior art describes the use of electro-luminescent materials as adjuncts to conventional lighting; for example U.S. Pat. No. 6,168,282, issued Jan. 2, 2001 to Chien. In this case, because of the limited light output from the electro-luminescent material, electro-luminescent devices are not useful for primary lighting. EP1120838A2, published Aug. 1, 2001 describes a method for mounting multiple organic light emitting devices on a mounting substrate to create an area illumination light source. However, this approach of mounting multiple light sources on a substrate increases the complexity and hence the manufacturing costs of the area illumination light source.
There is a need therefore for an improved, solid-state flat-panel area illumination device providing robust illumination with high brightness and a simplified manufacturing process.